Tension control including motor speed regulation system

ABSTRACT

This disclosure relates to a speed regulation system for a line speed pace motor for actuating strip material that is being wound or unwound in coil form by a reel motor. Diameter signals are generated which are a function of the instantaneous coil diameter D. Using field weakening for speed control of the reel motor, the coil has a defined diameter Do when the reel motor is at weakest field. Circuitry is arranged to receive the diameter signals and deliver control signals as a function of the instantaneous diameter for all diameters D&lt;/=Do. A speed regulation circuit for the line speed pace motor is connected to receive dual inputs, one being a speed command or reference signal, and the other being the control signals. The speed regulation circuit then delivers a constant speed signal to the line speed pace motor when D&gt;Do, and a progressively decreasing speed signal to the line speed pace motor for all magnitude of D&lt;/=Do, so that at weakest field of the reel motor, the line speed is reduced progressively as a function of the instantaneous diameter.

United States Patent 11 1 Pittner .1" TENSION CONTROL INCLUDING oronSPEED REGULATION SYSTEM John R. Pittner, Pittsburgh, Pa.

{73] Assignee: Westinghouse Electric Corporation,

Pittsburgh, Pa.

221 Filed: Feb. 4, 1972 211 Appl.No.:223,564'

{75] Inventor:

Primary ExaniinerT. E. Lynch Attorney- F. H. Henson,.l. J. Wood et al.

TENSION ROLLS l I l I l LINE SPEED PACE MOTOR FROM LINE SPEED CONTROLLER86 1 51 July 31, 1973 57 ABSTRACT This disclosure relates to a speedregulation system for a line speed pace motor for actuating stripmaterial that is being wound or unwound in coil form by a reel motor.Diameter signals are generated which are a function of the instantaneouscoil diameter D. Using field weakening for speed control of the reelmotor, the coil has a defined diameter Do when the reel motor is atweakest field. Circuitry is arranged to receive the diameter signals anddeliver control signals as a function of the instantaneous diameter forall diameters D Do. A speed regulation circuit for the line speed pacemotor is connected to receive dual inputs, one being a speed command orreference signal, and the other being the 1. control signals. The speedregulation circuit then delivers a constant speed signal to the linespeed pace motor when D Do, and a progressively decreasing speed sig-tnal to the line speed pace motor for all magnitude of D s Do, so that atweakest field of the reel motor, the line speed is reduced progressivelyas a function ofthe instantaneous diameter.

4 Claims, 3 Drawing Figures I 11c. REEL MOTOR K TACHOMETER GENERATOR R22 OPERATORS CONSCLE Do TENSION CONTROL INGILUDING MOTOR SPEEDREGULATION SYSTEM CROSS REFERENCE To RELATED-APPLICATION sAcnoaduNoorTHE INVENTION 1. Fieldof'the Invention- The invention relates toa'constant tension control system. for direct current reel drive motorsoperating to wind or unwind a coil of strip material moving alongaprocess line. I i

2. Description of the Prior Art The prior art has provideda variety oftechniques for controlling direct current reeldrive motors'so as toinsure' constant tension in a coil of strip material that is being woundor unwound. The speed of DC shunt motors is frequently controlled byfield wealting, the motor attaining its highest speed at theweakestfield setting. Usually, then the latter field setting is thecontrolling parameter, and motor operation is not permitted at higherspeeds. While it is true that for some motors, the manufacturer'sspecifications do permit higher speeds and overvoltage conditions, theseincreased operational rangesfor speed and voltage are for limitedperiods of time, and are-more-or less intended for'emergency situations,and not recommended for routine operations. i

The DC reel motor acts as a drag machine so that. it

tends to follow the line speed and produce allthe drag necessary. Whenthe reel motor is at weakest field, if the process line speedis highenough, the DC reel motor will run at both higher speed and voltage. Thepresent invention provides. a system for automatically enabling the linespeed to be reduced, if necessary, when the highest rated motor speed isattained.

SUMMARY OF'TI-IE INVENTION A speed regulation system for a line speedpace motor is provided for actuating strip material being input signal,the other being saidgcontrol signals, the

speed regulating means delivering a. constant speed sig: nal to saidline speed pace motor when D Do and. progressively decreasing speedsignals to said line speed pace motor for all magnitudes of D Do.

BRIEF DESCRIPTION' OF THE DRAWINGS FIG. 1 is a schematic illustratingthe speed regulation system of the invention in one environmentalsetting;

FIG. 2 is an electrical schematic showing the diameter memory anddiameter signals circuitry utilized in the speed regulatory system ofthe invention; and

a variable diameter D. The mandrel 12 is coupled,

through gearing shownsymbolically at 16, to'a-v DC reel drive motor 18'.A tachometer generator 20' is connected to the'shaft of motor 18. Theoutput signal of the tachometer generator is utilized at several pointsthroughout the system,but here in FIG. 1 it. is shown being coupled. tothe operator's console 22 to enable the reel drive motor speed to bemonitored. A line speed. pacer motor 24 sets the speed for the entireprocess line. Reel drive motor I-Sessentially acts as a drag machine inresponding to the strip line speed.

In order to understand the rationale upon which the invention rests, thefollowing mathematical analysis is presented. I I I In one: revolution,the calculated circumference of the reel:

' per minute gives the length of material wound or unwound per .unittime.

(2)-FPM 1r D (RPM/K where FPM the process line speed (feet per minute)RPM the speed of reel motor (revolutions per min- K, the gearingconstant a The reel motor speed is first controlled by. field weak.-ening. At weakest. field the process line speedv is FPMo, the reel.motor speed is RPMo, and the reel diameter is 'Do. I

a) FPMo =(1rD0- arm/K If the line speed is made directly diameter. Thenfor D 00 4 FPM K,D I

proportional to the In orderthen to insure thatthe reel motor speed RPMRPMo, solve equations (3) and-(7) for K (8) FPMo K =1rD0 RPMo' (9 K,=(1rDoRPMo/FIM0) (10) mo RPMo K, =(1rRPMo/K,) Equating equations (9) and(10) solving for K,

(12) K, (FPMo/Do) DESCRIPTION OF THE PREFERRED EMBODIMENT Before.beginning a description of the preferred embodiment some observationsare in order. The instant I invention system may be used wherever a 'DCreel shunt motor is operating at its highest speed and the process linespeed is high enough so that without an adjustment it would cause thereel motor to exceed its rated speed at weakest field; the inventionprovides automatic compensation of the line speed as a function of thereel diameter.

The invention may also be used advantageously with the teachings of thecopending application for Constant Tension Control System for a DC ReelDrive Motor" Ser. No. 2l4,808 filed on Jan. 3, 1972 in the name of JohnR. Pittner and assigned to the same assignee as the instant invention.

Briefly, the latter invention in order to achieve constant striptension, provides for flux control between full field and weak field. Atthe coil diameter Do (weak field), the system then switches to controlof the armature current as a function of the coil diameter, to maintainconstant tension, the flux being held constant. At this point the linespeed may have to be reduced, the operator accomplishing the adjustmentmanually. This invention may advantageously be employed to adjust theline speed automatically.

In order then to practice the invention, one must know D at alltimesyMoreover, since there are occasions when the process line must betemporarily stopped, it is imperative that the diameter D at the momentof stopping be remembered." The circuitry of FIG. 2 will accomplishthese objectives.

Referring now to FIG. 2,, the reel speed signal (R.P.M.)-obtained fromthe tachometer generator is applied as a divisor input to a divider 26.The line speed signal (which is a function of the line speed in feet perminute (FPM)) is fed as a dividend-input to the divider 26. The quotientoutput 28 from the divider 26 is applied to an operational amplifier,indicated generally at 30, through a resistor 32. Information concerningthe start-up diameter of the coil 14 is applied to the amplifier 38 bymeans of a potentiometer 34 connected between a positive source of DCvoltage 24V) and ground, the slider being serially connected throughnormally open'contacts ICRI and resistor 36 to the amplifier input.

The, relays described in this application are identifie as follows. Thecoils are numbered ICR, 2CR, and 3CR. The contact pairs associated withthe respective coils are identified for example as 3CR1, 3CR2, 3CR3, the3 preceding the CR identifying the third contact relay, the numeralfollowing CR identifying the particular contacts viz. first (I) second(2), third (3); the bar be neath the identifying numeration indicatesthat the contact is normally closed, while no bar signifies that thecontacts are'normally open.

The operational amplifier 30 includes a high gain amplifier 38 having afeedback path containing contacts 3CR1 and 1CR2, in parallel with animpedance 40. The output of the amplifier 38 is connected to a motoroperated potentiometer indicated generally at 42, having potentiometers46, 48 the slider contacts of which are arranged to be rotationallydisplaced in unison in accordance with the rotation of the motor 44. Theslider of potentiometer 46 is connected to the input of the amplifier 38through resistor 50. The slider of potentiometer 48 is connected throughthe contacts 3CR2 to the output 52. The slider of potentiometer 48 maybe used to provide a signal for the operator to monitor when Do isreached, or a separate" potentiometer may 0 be mounted on the commonshaft of the motor operated potentiometer 42. Completing the descriptionof the diameter memory and signal circuitry, the relay lCR is energizedthrough contacts 54which are momentarily closed on signal from the logiccircuitry 56. The diameter Signal D of FIG. 2 is applied as an input D,as shown in FIG. 3. Where a rewind reel is also to be monitored, adiameter memory and diameter signal circuit identical to FIG. 2, is usedto provide the signal shown at D, in FIG. 3. I I Referring now to FIG.3, a line speed reference potentiometer is indicated at 58, thepotentiometer being connected between a source of negative potential(-24vDC) and ground. ,(This potentiometer may be adjusted from theoperators console 22). The slider of the potentiometer $8 is connectedto an operational amplifier indicated generally at 60, the amplifier 60having resistors 62,64. A load. resistor 66 is connected between thenodes identified as A, and A The diameter signal D, is applied toa-potentiometer 68, the-slider of which is connected to the cathode of adiode having its anode connected to node A Similarly, thediameter'signal D, is applied to 'poten'tiometer 72, the slider of whichis connected to the cathode of a diode 74, having its anode connected tonode A,.

A non-inverting amplifier 76 having -unit gain is inserted between nodeA, and. anoperational amplifier indicated generally at 78. The amplifier78 has resistors identified at 80,82. The output of the operationalamplifier 78 is applied to a line ramp generator 84 which develops aramp signal for application to the line speed controller 86. Thecontroller 86 is applied to the line speed pace motor 24 to control thespeed thereof, and hence the line strip speed.

OPERATIONS 7 As stated earlier, the invention is applicable wheneverthe' process line speed must be controlled becauseof the fact that thereel motor is operating at its highest by adjustment of thevpotentiometer 58. The required tension for the strip material is alsoadjusted by means not shown since it forms no part of this invention.The diameter size of the reel to be payed out is known to'the operatorand-this information requires a certain definite setting forthe'potentiometer 34 (FIG. 2). In the steel mill, the reel 14 '(FIG. 1)is first mounted on a i The line speed of the process is set by theoperator 7 mandrel 12 which is segmented and adapted to collapse so asto fit inside and adopted itself to various inner reel diameters. Whenthe mandrel 12 is released it presses outward forcing itself tightlyagainst the inner diameter of the reel. By means of sensors (not shown)the logic circuitry 56 (FIG. 2) then sends the signal momentarilyclosing contacts 54 thereby connecting power to relay ICR. Upon theenergization of relay lCR: (a) contacts lCRl (FIG. 2) close, and thevoltage corresponding to the operator settingfor potentiometer 34 isapplied as an input to operational amplifier 30, and (b) contacts 1CR2open removing the short on the amplifier 30 to enable the actuation ofthe motor 44. The come-to-rest setting of the potentiometers 46,48provides an analog voltage representative of the initial diameter of thereel 14, V

At low speeds of the reel motor 18, the quotient output 28 of thedivider 24 is unreliable. (Accordingly, the divider is not utilizeduntil the reelmotor 18 reaches sufficient speed to make the quotientoutput 28 reliable.) In the meanwhile the output signal D is that of theinitial diameter. As the reel motor 18 increases in speed, a point isreached where the quotient output 28 of the divider 26 is reliable; thispoint is identifiable in that the armature A (FIG. 2) develops a voltageof a sufficient magnitude to energize relay 2CR. The contacts of 2CR1close, applying power to relay 3CR. The energization of relay 3CRperforms three functions: (a) 3CR1 opens removing the short on theoperational amplifier 30 to cause the motor operated potentiometer 42 tobe actuated; (b) contacts 3CR2 open isolating the diameter memory, and(c) contacts 3CR3 close so that the quotient signal 28 is fed directlyto the output 52. Thus the setting of the slider of potentiometer 48serves to remember the diameter D should the process line be stopped forany reason. Also it should be observed that the quotient signal 28 isfed directly to the output 52 through now closed contacts 3CR3.

A brief consideration of the nature of the quotient signal 28 is inorder, [(FPM ft./min.)/RPM('revolutions/min.)] (number of feet/lrevolution) l revolution the instantaneous circumference of the reel.Since the circumference 1r diameter of reel, the number of feet dividedby 11- equals the diameter of the coil. As the reel is payed out thediameter is constantly being reduced, while conversely during the windup of mode the diameter is continuously increasing.

Motors are designed to operate between full field and weakest field toprovide a range from base speed to the highest speed. Depending upon themanufacturers specifications, operation beyond the weakest field may bepermitted for certain voltages ranges and for limited periods of time.

With the weakest field setting, the motor is at maximum speed. Briefly,the'line pace setter motor 24 sets the process line speed. The reelmotor 18 is essentially a drag machine At weak field, the motor 18 willrun at higher speeds and voltage to accommodate the line speed and thiscould possibly cause electrical and mechanical damage to the motor.

The diameter signal D and D, if it is used) is applied to system of FIG.3. When the reel motor is at its highest speed the reel 14 has a finitediameter defined as Do. The setting of potentiometer 58 and themagnitude of resistors 62 and 64 establishes a voltage level at Node Al.The potentiometers 68 and 72 are ad justed (K adjustment) so that thevoltage matches the voltage at node Al when the signals Dl(and D2) areat the control diameter Do. If equation 12 is solved so that: l(FPMo/DoK the diode 68 (or 72) will conduct when the ratio (FPMo/DoK isa l and will be blocked when the ratio is 1.

When the reel diameter D Do, the diode is blocked (Similarly if therewind reel D D0 diode 74 is blocked). The line space pacer motor is nowrunning at the speed set by the operator by means of potentiomete r 58.When either diameter signal D 5 Do, the associated diode 70 or 74conducts so that the voltage at node A, decreases proportionally,causing the output of the operational amplifier 78 to decreaseproportionally, and thus the line speed reference signal decreasesproportionally, so that the line speed pace motordecreasesproportionally as a function of the reel diameter.

Some idea of the magnitude of the time that is lost may be had from aconsideration of the following calculations for a pay off coil. Assumethe following conditions:

Line Data Top Speed 1,500 FPM Pay off range 70 10 inches Thickness ofmaterial 0 .005 in.

D0 24 inches Definitions A strip thickness (in feet) I time in minutes(RPMo/Kl) RPMo Assume a DC shunt motor having a field weakening range3:1. We shall compute the time required to pay out the coil from 24inches to 10 inches running at the top speed of 1,500 RPM, and thencalculate the time required to perform the same task when the line speedis decreased as a function of diameter D. Starting at Do =24 inches andRPM 1,500 RPM at D D0 (13)D(t)= Do RPMc 2 At att=t D=Dl 7 (t1) D, D0RIM: 2A1,

solve for t,

(= t =(D0 DI/ZARPMC) But from equation (3) and definition for RPMc.

(l6) FPMo Do 1r RPMc (l7) RPMc (FPMo/Do 1r) Substituting equation (17)in equation (15):

9 (l8) t 1)0 0,) Do 1r/21r FPMO] Let L0 the total length unwound from Do24 inches to D, 10 inches If this length L0 were run at FPMo, neglectingdeceleration, the time to would be (21) to =(L0/FPMO) (22) to =(1'r/4A)(D0 D )/FPM0 The extra time required is A! t, to

(25) 1'|'(2D0 DoD )(D D /4 A FPMo (26) 11' (D0 2DOD, D )/4A FPMo (27) 1r(D0 D,) /4A FPMo In the example given A 0.005 in 4.16 X feet D0 24inches 2 feet D 10 inches 0.835 feet FPMo 1,500 ft/min Substituting inequation (27) 1.7 minutes i 1 claim: 1. A speed regulation system for aline speed pace motor for actuating strip material being wound orunwound in coil form by a reel motor comprising:

means for providing successive diameter signals which are a function ofthe instantaneous coil diameter D, the coil having a finite diameter DoWhen said reel motor is at the weakest field flux, said diameter signalmeans comprising divider means having dividend and divisor inputs and aquotient output, said inputs being connected to receive a line speedsignal and a reel motor rotational speed signal respectively, thequotient output being a function of, the instantaneous diameter D;

means coupled to said diametersignal means, to receive said diametersignals and deliver control signals as a function of the instantaneousdiameter when D Do; and

means for regulating the speed of said line speed pace motor connectedto receive dual inputs, the one being a reference speed input signal,the other being said control signals, and for delivering a constantspeedsignal to said line speed pace motor when D Da, and progressivelydecreasing speed signals to said line speed pace motor for all magnitudeof D D0.

2. A speed regulation system for a line speed pace motor for actuatingstrip material being wound or unwound in coil form by a reel motorcomprising:

means for providing successive diameter signals which are a function ofthe instantaneous coil diameter D, the coil having a finite diameter D0when said reel motor is at the weakest field flux; means coupled to saiddiameter signal means, to receive said diameter signals and delivercontrol signals when D D0, said control signal means comprising apotentiometer and a diode, said diameter signals being applied acrosssaid potentiometer, means for regulating the speed of said line speedpace motor connected to receive dual inputs, said potentiometer having aslider connected to one electrode of said diode, the other electrodebeing connected to one of said dual inputs to said regulating speedmeans, the slider being adjusted so that the diode is forward biasedwhen D Do, the other dual input being a reference speed input signal,said regulating speed means delivering a constant speed I signal to saidline speed pace motor when D Da, f and progressively decreasing speedsignalsto said line speed pace motor for all magnitudes of D Do. 3. Aspeed regulation system for a line speed pace 0 motor for actuatingstrip material being wound or unwound in coil form by a reel motorcomprising:

means for providing successive diameter signals which are a function ofthe instantaneous coil diameter D, the coil having a finite diameter D0when said reel motor is at the weakest field flux; means coupled to saiddiameter signal means, to receive said diameter signals and delivercontrol signals as a function of the instantaneous diameter when D D0,and means for regulating the speed of said line speed pace motorcomprising an operational amplifierhaving signals to said line speedpacefor all magnitudes of D Do. a

4. A speed regulation system for a line speed pace motor for actuatingstrip material being wound or unwound in coil form by a reel motorcomprising a. means for providing successive diameter signals D,

the coil having a finite diameter D0 when said reel motor is at theweakest field flux, said diameter signal means comprising divider meanshaving dividend and divisor inputs and a quotient output, said inputsbeing connected to receive a line speed signal and a reel motorrotational speed signal respectively, the quotient output being afunction of the instantaneous diameter D;

b. means coupled to said diameter signal means, to receive said diametersignals and deliver control signals as a function of the instantaneousdiameter when D .5 Do, said control signal means comprising apotentiometer and a diode, said diameter signal being applied acrosssaid potentiometer, said potentiometer having a slider connected to oneelectrode of said diode, the slider being adjusted so that the diode isforward biased when D 5 Do; and means for regulating the speed of saidline speed pace motor. connected to receive dual inputs, the one being areference command speed input signal, the other being connected to theother electrode of said diode to receive said control signals, saidspeed regulating means delivering a constant speed signal to said linespeed pace motor when D Da, and a progressively decreasing speed signalto said line speed pace motor for all magnitude of D E D0.

means, said regulating speed means deliveringa

1. A speed regulation system for a line speed pace motor for actuatingstrip material being wound or unwound in coil form by a reel motorcomprising: means for providing successive diameter signals which are afunction of the instantaneous coil diameter D, the coil having a finitediameter Do when said reel motor is at the weakest field flux, saiddiameter signal means comprising divider means having dividend anddivisor inputs and a quotient output, said inputs being connected toreceive a line speed signal and a reel motor rotational speed signalrespectively, the quotient output being a function of the instantaneousdiameter D; means coupled to said diameter signal means, to receive saiddiameter signals and deliver control signals as a function of theinstantaneous diameter when D < OR = Do; and means for regulating thespeed of said line speed pace motor connected to receive dual inputs,the one being a reference speed input signal, the other being saidcontrol signals, and for delivering a constant speed signal to said linespeed pace motor when D> Do, and progressively decreasing speed signalsto said line speed pace motor for all magnitude of D < OR = Do.
 2. Aspeed regulation system for a line speed pace motor for actuating stripmaterial being wound or unwound in coil form by a reel motor comprising:means for providing successive diameter signals which are a function ofthe instantaneous coil diameter D, the coil having a Finite diameter Dowhen said reel motor is at the weakest field flux; means coupled to saiddiameter signal means, to receive said diameter signals and delivercontrol signals when D < or = Do, said control signal means comprising apotentiometer and a diode, said diameter signals being applied acrosssaid potentiometer, means for regulating the speed of said line speedpace motor connected to receive dual inputs, said potentiometer having aslider connected to one electrode of said diode, the other electrodebeing connected to one of said dual inputs to said regulating speedmeans, the slider being adjusted so that the diode is forward biasedwhen D < or = Do, the other dual input being a reference speed inputsignal, said regulating speed means delivering a constant speed signalto said line speed pace motor when D>Do, and progressively decreasingspeed signals to said line speed pace motor for all magnitudes of D < or= Do.
 3. A speed regulation system for a line speed pace motor foractuating strip material being wound or unwound in coil form by a reelmotor comprising: means for providing successive diameter signals whichare a function of the instantaneous coil diameter D, the coil having afinite diameter Do when said reel motor is at the weakest field flux;means coupled to said diameter signal means, to receive said diametersignals and deliver control signals as a function of the instantaneousdiameter when D < or = Do, and means for regulating the speed of saidline speed pace motor comprising an operational amplifier having oneterminal to receive a reference input signal and a second terminalconnected to said control signal means, said regulating speed meansdelivering a constant speed signal to said line speed pace motor whenD>Do, and progressively decreasing speed signals to said line speed pacefor all magnitudes of D < or = Do.
 4. A speed regulation system for aline speed pace motor for actuating strip material being wound orunwound in coil form by a reel motor comprising a. means for providingsuccessive diameter signals D, the coil having a finite diameter Do whensaid reel motor is at the weakest field flux, said diameter signal meanscomprising divider means having dividend and divisor inputs and aquotient output, said inputs being connected to receive a line speedsignal and a reel motor rotational speed signal respectively, thequotient output being a function of the instantaneous diameter D; b.means coupled to said diameter signal means, to receive said diametersignals and deliver control signals as a function of the instantaneousdiameter when D < or = Do, said control signal means comprising apotentiometer and a diode, said diameter signal being applied acrosssaid potentiometer, said potentiometer having a slider connected to oneelectrode of said diode, the slider being adjusted so that the diode isforward biased when D < or = Do; and c. means for regulating the speedof said line speed pace motor connected to receive dual inputs, the onebeing a reference command speed input signal, the other being connectedto the other electrode of said diode to receive said control signals,said speed regulating means delivering a constant speed signal to saidline speed pace motor when D>Do, and a progressively decreasing speedsignal to said line speed pace motor for all magnitude of D < or = Do.